1. Field of the Invention
The present invention relates generally to a friction torque device, and more particularly to a friction torque device that is adjustable to compensate for wear on a friction surface within the device.
2. Description of the Related Art
A friction torque device, such as a friction clutch or brake, provides a releasable torsional connection between a motor vehicle engine flywheel and an associated transmission. In a friction clutch, torque is transmitted from a driving member to a driven member, each member rotating about an axis. The driven member is interposed between the driving member and a pressure plate. In normal operation, a release assembly cooperates with the pressure plate to selectively move the pressure plate axially towards the driven member in order to engage and disengage the clutch. As wear occurs on a friction surface of the driven member, the pressure plate must be moved an additional axial increment to engage the driven member with the driving member. The relative position of the pressure plate must therefore be compensated internally for this additional increment of movement.
It is known in the art to provide a clutch with an automatic adjustment mechanism that compensates for driven disc wear and maintains the clutch engagement force. One type of known adjustment mechanism relies on the relative rotation of two annular cams, each having inclined cam surfaces in engagement with each other. The relative rotation of the cams compensate for wear of the friction material. More particularly, the cams are biased to rotate in a direction that increases a combined height or thickness of the cam portions. The rotative biasing force is induced by a torsional biasing spring functionally disposed between the two cams.
Over time, the friction surfaces in a clutch wear to a point the driven disks need to be replaced, requiring that the clutch be disassembled and remanufactured. Because many motor vehicle configurations are operable with manually adjustable clutches or simply do not justify the added expense of automatic adjustment, many remanufactured automatically adjustable clutches go unsold or are otherwise not utilized. Thus, there is a demand for automatically adjusting clutches that are operable manually or are easily remanufactured into manually adjustable clutches for use in applications that do not functionally require or economically justify automatic adjustment.
A friction torque device includes an adjustment mechanism for adjusting the device in response to wear on a friction surface of a driven member within the device. The friction torque device transmits torque from a driving member to the driven member, which is coupled to an axially extending driven shaft. A cover is secured to the driving member for rotation therewith. A pressure plate and the driven member are sandwiched between the driving member and the cover. A release assembly extends circumferentially about the driven shaft.
In one embodiment of the present invention, the adjustment mechanism includes a first annular cam ring, a second annular cam ring adjacent the first annular cam ring and an adjustment limiting member for controlling adjustment. Opposed faces of the cam rings include corresponding annular ramped surfaces for camming. The cam rings rotate with respect to each other for axial displacement of the cam rings. The adjustment is a direct function of increased movement of the pressure plate due to wear on friction surfaces, which is triggered by a pin or pin assembly that cooperates with the pressure plate. The increment of wear on the friction surface of driven member is directly translated into a gap between the annular cam rings. The cam rings cam against each other to displace this gap when the clutch is fully disengaged. The adjustment limiting member is selectively engagable with the first cam ring to inhibit rotation thereof and disengageable with the first cam ring to permit adjustment of the friction device.
In another embodiment of the present invention, the adjustment mechanism includes a first annular ring, a second annular ring adjacent the first annular ring and an adjustment limiting member for controlling adjustment. Opposed faces of the first and second rings include corresponding threaded surfaces that function to displace the second ring upon rotation of the first ring. The increment of wear on the friction surface of driven member is directly translated into a gap between the first and second rings. The adjustment limiting member is selectively engagable with the first ring to inhibit rotation thereof and disengageable with the first ring to permit adjustment of the friction device.
In another embodiment of the present invention, the adjustment mechanism includes an adjusting ring having an adjusting thread at an outer peripheral surface and the cover having a cover thread at an inner peripheral surface. The adjusting thread mates with the cover thread such that the adjusting ring is selectively rotatable relative to both a pressure plate and to the cover, and is moveable in an axial direction relative to the cover in response to rotation. The adjusting ring controls an axial displacement of the pressure plate relative to the cover as a function of relative rotative position.
These and other features of the present invention can be best understood from the following specification and drawings, of which the following is a brief description.